Currently, nearly all commercially available VCSELs used for fiber communication are 850-nm AlGaAs-based devices. However, the capacity and reach of these networks would be improved by using long-wavelength VCSELs (1300 and 1550 nm) constructed from InP-based materials. However, construction of VCSELs that emit at these longer wavelengths is hampered by the absorption of the generated light, particularly in the p-type material layers of the VCSEL.
A conventional VCSEL is a p-i-n diode structure having DBR mirrors above and below the active region. The top mirrors are constructed from a large number of layers of p-type material in which the index of refraction of the layers alternates between two values. The bottom mirror is similarly constructed from a large number of layers of an n-type material in which the index of refraction of the layers alternates between two values. The mirrors define the laser cavity that is roughly one half p-type semiconductor material. At long wavelengths, the p-type material absorption is significant, and hence, designs in which the amount of p-type material, through which the light must pass, is substantially reduced are needed.